Potentiometric position transducers are commonly used to measure or detect position or displacement of a moveable component. A voltage is applied between electrical contacts positioned at opposite ends of a resistive track. A third electrical contact, moveable back and forth over the resistive strip by suitable linkage means, provides an output voltage variable with its position on the track. Advantages of potentiometric position transducers typically include a large output signal voltage, good resolution, relatively low noise to signal ratio and good durability, at least under low vibration conditions.
In a rotary transducer, the resistive element can be provided as a segment of a ring. When a voltage is applied between the two resistor ends, a central sliding contact can pick up a voltage representing the angle of rotation of the shaft or rotor on which the sliding contact is mounted. In a linear transducer, the resistive element typically is an elongate rectangular strip and the central sliding contact is attached to a rod which moves linearly. The voltage signal from the energized resistor is a measure of rod linear position. A rotary potentiometer is illustrated in U.S. Pat. No. 4,621,250 to Echasseriau et al, wherein a stationary resistive track is provided on the cylindrical inside surface of a case or housing. A resilient wiper is carried by a rotor rotatably mounted in the housing. The wiper contacts the resistive track during operation of the potentiometer. A spring placed between the case and the rotor biases the rotor to a rest position. Similarly, in U.S. Pat. No. 4,355,293 to Driscoll a rotary potentiometer is disclosed for measuring the position of the throttle blade of an internal combustion engine. A flexible resistive element is cemented to the arcuate inner wall of a housing. A potentiometric position transducer employing linear resistive strips is shown in U.S. Pat. No. 4,693,111 to Arnold et al, wherein three elongate resistive strips are laid out in parallel and used simultaneously for enhanced position signal resolution.
A recognized problem associated with potentiometric position transducers involves wear of the electrically resistive track. Typical film type resistive tracks may be designed to withstand millions of passes or cycles of the sliding electrical contact. Vibration of the sliding contact on the resistive track, however, causes accelerated wear. A 10 Hz vibration, for example, achieves one million cycles in less than 30 hours. In a potentiometric position transducer used to measure throttle position in a motor vehicle engine, for example, the sliding electrical contact will remain in a localized area of the resistive track while the car is driven at a constant speed on flat terrain. Vibration of the electrical sliding contact on the resistive element can cause wear on such localized area. The present invention addresses the problem of localized wear of the resistive track in a potentiometric position transducer.